JP4033072B2 - Control device for gas concentration sensor - Google Patents

Description

  The present invention relates to a gas concentration sensor control device, and more particularly to a gas concentration sensor control device suitable for controlling a gas concentration sensor disposed in an exhaust passage of an internal combustion engine.

  Conventionally, as disclosed in, for example, Japanese Patent Application Laid-Open No. 2000-28575, an apparatus including an oxygen sensor in an exhaust passage of an internal combustion engine is known. In this device, the oxygen sensor generates an output corresponding to the oxygen concentration in the exhaust gas flowing through the exhaust passage. The oxygen concentration in the exhaust gas has a correlation with the exhaust air-fuel ratio. Therefore, according to the conventional apparatus, information on the exhaust air / fuel ratio can be obtained based on the output of the oxygen sensor.

  This device also has a function of detecting the element impedance of the oxygen sensor by changing the voltage V0 applied to the oxygen sensor from the reference voltage to the sweep voltage. When a change of ΔV0 occurs in the applied voltage V0, a change ΔI corresponding to the element impedance Rs occurs in the current I flowing therethrough. For this reason, the conventional apparatus calculates the element impedance Rs based on the voltage change ΔV0 and the current change ΔI that are generated when the applied voltage V0 is switched from the reference voltage to the sweep voltage.

JP 2000-28575 A

  As described above, the conventional apparatus acquires information on the exhaust air / fuel ratio based on the output of the oxygen sensor and detects the element impedance by applying a sweep voltage to the oxygen sensor. While the sweep voltage is applied to the oxygen sensor, the output is a value affected by the sweep voltage. For this reason, while the sweep voltage is applied, the output of the oxygen sensor becomes a value that does not correspond to the exhaust air-fuel ratio.

  The oxygen sensor includes an impedance component and a capacitance component. For this reason, the output of the oxygen sensor does not return to a value corresponding to the exhaust air / fuel ratio for a while after the application of the sweep voltage is stopped. For this reason, in the above-described conventional apparatus, after the sweep voltage is applied to the oxygen sensor in order to detect the element impedance, the exhaust air-fuel ratio state is erroneously detected until the influence of the sweep voltage disappears. Things can happen.

  The present invention has been made to solve the above-described problems, and is a gas concentration sensor that realizes both a function of detecting an element impedance of a gas concentration sensor and a function of accurately detecting information related to an exhaust air / fuel ratio. An object of the present invention is to provide a control device.

In order to achieve the above object, a first invention is a control device for a gas concentration sensor that emits an output having a correlation with an oxygen concentration in a gas to be detected.
Impedance detection means for applying an impedance detection voltage to the gas concentration sensor to detect an element impedance of the gas concentration sensor;
After the impedance detection voltage is applied to the gas concentration sensor, the same voltage as that generated by the gas concentration sensor, or a voltage opposite to the impedance detection voltage as viewed from the voltage, is applied for a predetermined period. Reverse voltage applying means for applying to the gas concentration sensor;
And reverse voltage application period setting means for setting the predetermined period to be longer as the element impedance is larger .

In a second aspect based on the first aspect , the reverse voltage application period setting means sets the predetermined period shorter as the difference between the voltage generated by the gas concentration sensor and the impedance detection voltage is smaller. It is characterized by doing.

A third invention is a control device for a gas concentration sensor that emits an output having a correlation with an oxygen concentration in a gas to be detected.
Impedance detection means for applying an impedance detection voltage to the gas concentration sensor to detect an element impedance of the gas concentration sensor;
Data discarding means for discarding the output of the gas concentration sensor for a predetermined period after the impedance detection voltage is applied to the gas concentration sensor;
Data discard period setting means for setting the predetermined period to be longer as the element impedance is larger .

A fourth invention is a control device for a gas concentration sensor that emits an output having a correlation with an oxygen concentration in a gas to be detected.
Impedance detection means for detecting an element impedance of the gas concentration sensor by applying an impedance detection voltage to the gas concentration sensor at predetermined intervals;
Impedance detection interval setting means for setting the predetermined interval longer as the element impedance is larger;
It is characterized by providing.

The fifth invention is the fourth invention, wherein
Output acquisition period setting means for setting a period from when a predetermined period has elapsed after detection of the element impedance to when the impedance detection voltage is applied again to the gas concentration sensor as an output acquisition period of the gas concentration sensor When,
An output non-acquisition period setting means for setting the predetermined period to be longer as the element impedance is larger;
It is characterized by providing.

The sixth invention is the fourth or fifth invention, wherein
The impedance detection interval setting means, the area wherein the element impedance is equal to or greater than a predetermined threshold value, which is set longer the predetermined distance as the element impedance is large,
Low-impedance detection interval setting means for setting the predetermined interval longer than a predetermined interval set when the element impedance matches the predetermined threshold in a region where the element impedance is lower than the predetermined threshold. It is characterized by providing .

Since the present invention is configured as described above, the following effects can be obtained.
According to the first invention, after the impedance detection voltage is applied to the gas concentration sensor, the output of the gas concentration sensor is quickly converged to the voltage generated by itself, that is, the output corresponding to the exhaust air-fuel ratio. be able to. Therefore, according to the present invention, it is possible to realize both the function of detecting the element impedance and the function of accurately detecting information related to the exhaust air / fuel ratio. Further, according to the present invention, the voltage application period (predetermined period) for eliminating the influence of the gas concentration sensor is larger when the element impedance of the gas concentration sensor is larger and the influence of the impedance detection voltage needs longer. Can be lengthened. For this reason, according to the present invention, the influence of the impedance detection voltage can be eliminated efficiently in a short time.

According to the second invention, the difference between the voltage generated by the gas concentration sensor and the impedance detection voltage is so small that the influence of the impedance detection voltage can be easily extinguished in a short period of time. The application period (predetermined period) can be shortened. For this reason, according to the present invention, the influence of the impedance detection voltage can be eliminated efficiently in a short time.

According to the third aspect , the output of the gas concentration sensor can be discarded during a predetermined period when the influence of the impedance detection voltage appears in the output of the gas concentration sensor. For this reason, according to the present invention, it is possible to realize both the function of detecting the element impedance and the function of accurately detecting information related to the exhaust air / fuel ratio. Further, according to the present invention, the period (predetermined period) for discarding data can be lengthened so that the element impedance of the gas concentration sensor is large and the influence of the impedance detection voltage is likely to appear for a long time. Therefore, according to the present invention, erroneous detection of the exhaust air / fuel ratio state based on the output of the gas concentration sensor can be effectively prevented.

According to the fourth aspect of the present invention, the impedance detection voltage application interval (predetermined interval) can be increased as the element impedance of the gas concentration sensor increases. For this reason, according to the present invention, it is possible to appropriately ensure a period in which the output of the gas concentration sensor correctly corresponds to the state of the exhaust air-fuel ratio regardless of the element impedance.

According to the fifth aspect of the invention, the output acquisition period can be started from the end of the period (predetermined period) in which the influence of the impedance detection voltage appears on the output of the gas concentration sensor. The predetermined period can be lengthened as the element impedance is large and the influence of the impedance detection voltage is likely to remain for a long time. For this reason, according to the present invention, it is possible to ensure a period in which the output of the gas concentration sensor correctly corresponds to the exhaust air-fuel ratio regardless of the element impedance as the output acquisition period.

According to the sixth aspect, in the region where the element impedance is below the predetermined threshold, the impedance detection voltage application interval (predetermined interval) can be made longer than when the element impedance matches the predetermined threshold. That is, according to the present invention, the detection frequency of the element impedance can be lowered under the condition that the element impedance is low and a large current flows along with the detection of the impedance. For this reason, according to the present invention, it is possible to effectively prevent the gas concentration sensor from being excessively damaged under a condition where the element impedance is low.

  Embodiments of the present invention will be described below with reference to the drawings. In addition, the same code | symbol is attached | subjected to the element which is common in each figure, and the overlapping description is abbreviate | omitted.

Embodiment 1 FIG.
[Description of circuit configuration]
FIG. 1 is a diagram for explaining the configuration of the first embodiment of the present invention. As shown in FIG. 1, the system of this embodiment includes an oxygen sensor 10 and an ECU (Electronic Control Unit) 20. In the present embodiment, the oxygen sensor 10 is disposed in the exhaust passage of the internal combustion engine, and sensor output corresponding to the oxygen concentration in the exhaust gas, more specifically, whether the exhaust air-fuel ratio is rich or lean. Assume that a sensor output is generated.

  In FIG. 1, the oxygen sensor 10 is equivalently shown as including an impedance component and an electromotive force component. That is, the oxygen sensor 10 is an electromotive force type sensor that generates a voltage corresponding to the oxygen concentration in the gas to be detected. In the present embodiment, the oxygen sensor 10 and the ECU 20 are connected such that the terminal OX1B side is the high voltage side and the terminal E2 side is the low pressure side. The ECU 20 can determine whether the exhaust air-fuel ratio is rich or lean by looking at the voltage generated between the OX1B terminal and the E2 terminal.

  The element impedance Rs of the oxygen sensor 10 has temperature characteristics, and becomes smaller as the oxygen sensor 10 becomes higher in temperature. In order for the oxygen sensor 10 to function normally, it is necessary to control the temperature of the oxygen sensor 10 to the activation temperature. Since the temperature of the oxygen sensor 10 has a correlation with the element impedance Rs, it is convenient that the element impedance Rs can be accurately detected when the temperature is controlled to the above active temperature. Further, if the element impedance Rs can be accurately detected, it is possible to perform an abnormality diagnosis of the oxygen sensor 10 from the value. Thus, the oxygen sensor 10 has a demand for accurately detecting the element impedance Rs.

  The ECU 20 has a function of accurately detecting the element impedance Rs of the oxygen sensor 10 in response to the above request. In other words, the ECU 20 used in the present embodiment has a function of acquiring information related to exhaust air / fuel based on a voltage generated by the oxygen sensor 10 itself (voltage generated between the OX1B terminal and the E2 terminal), and the oxygen sensor 10. This unit has both the function of detecting the element impedance Rs. Hereinafter, the circuit configuration and function of the ECU 20 will be described in detail.

  The ECU 20 includes a first switch element 22. A constant voltage (power supply voltage) of 5V is supplied to the first switch element 22. The gate of the first switch element 22 communicates with the first port 24. The ECU 20 turns on the first switch element 22 by issuing an ON command to the first port 24 as necessary.

  The first switch element 22 is connected to the first sampling point 28 via the second resistor 26. The first sampling point 28 is electrically connected to the external terminal OX1B of the ECU 20 via the first resistor 30, and is electrically connected to the external terminal E2 of the ECU 20 via the first capacitor 31.

  The first sampling point 28 is connected to the first AD converter (ADC1) 32 through a filter circuit having a small time constant. The filter circuit includes two resistors 34 and 36 connected in series, and a capacitor 38 disposed between the input terminal of the first AD converter 32 and the ground line. Between the two resistors 34 and 36, a diode 40 for guarding the potential at the connection point to 5V or less is connected.

  The first AD converter 32 can convert an analog signal supplied to its input terminal into a digital signal and output it. The potential of the first sampling point 28 is supplied to the input terminal of the first AD converter 32 via the filter circuit having a small time constant described above. Therefore, the first AD converter 32 can digitize and output the potential of the first sampling point 28 with high accuracy even when the potential changes at a high frequency. As will be described later, the ECU 20 recognizes the digital signal generated by the first AD converter 32 under a predetermined condition as the potential of the first sampling point 28 and uses it for the detection process of the element impedance Rs.

  A second switch element 42 is connected to the first sampling point 28 via a third resistor 41. A second port 44 is connected to the gate of the second switch element 42. The ECU 20 turns on the second switch element 42 by issuing an ON command to the second port 44 as necessary. Therefore, the ECU 20 can cause the first sampling point 28 to be connected to the external terminal E2 via the third resistor 41 by generating an ON command at the second port 44.

  In the ECU 20, a second sampling point 50 is formed between the first resistor 30 and the external terminal OX1B. One end of an output detection resistor 52 arranged in parallel with the oxygen sensor 10 is connected to the second sampling point 50. The output detection resistor 52 has a sufficiently large impedance compared to the element impedance Rs of the oxygen sensor 10. Therefore, when the power supply voltage is not supplied to the second sampling point 50 (when the first switch element 22 is OFF), a voltage corresponding to the electromotive force of the oxygen sensor 10 is generated at the second sampling point 50. . When the power supply voltage is supplied to the second sampling point 50 (when the first switch element 22 is ON), a voltage corresponding to the product of the current I flowing through the oxygen sensor 10 and the element impedance Rs is Occurs at the second sampling point 50.

  A second AD converter (ADC2) 54 is connected to the second sampling point 50 through a filter circuit having a small time constant. The above filter circuit includes two resistors 56 and 58 connected in series, and a capacitor 60 disposed between the input terminal of the second AD converter 54 and the ground line. Between the two resistors 56 and 58, a diode 62 for guarding the potential at the connection point to 5 V or less is connected.

  The second AD converter 54 can convert an analog signal supplied to its input terminal into a digital signal and output it. The second sampling point 50 is connected to the input terminal of the second AD converter 54 via the filter circuit having a small time constant as described above. Therefore, the second AD converter 54 can digitize and output the potential of the second sampling point 50 with high accuracy even when the potential changes at a high frequency. As will be described later, the ECU 20 recognizes the digital signal generated by the second AD converter 54 under a predetermined condition as the potential of the second sampling point 50 and uses it for the detection process of the element impedance Rs.

  A third AD converter (ADC 3) 68 is further connected to the second sampling point 50 through a filter circuit including a resistor 64 and a capacitor 66. The filter circuit provided in the previous stage of the third AD converter 68 has a sufficiently large time constant, and allows only the low frequency component of the voltage at the second sampling point 50 to pass through. For this reason, the third AD converter 68 can accurately generate a digital signal corresponding to a steady voltage value at the second sampling point 50 without being affected by noise or the like. As will be described later, the ECU 20 recognizes a digital signal generated by the third AD converter 68 under a predetermined condition as an output signal of the oxygen sensor 10 and uses it for the detection process of the oxygen concentration in the gas to be detected.

[Explanation of ECU operation]
(Detection process of oxygen concentration information)
The ECU 20 turns off the first port 24 except when trying to detect the element impedance Rs of the oxygen sensor 10. If the first port 24 is OFF, the first switch element 22 is OFF, and the potential of the second sampling point 50 is constantly a value corresponding to the electromotive force of the oxygen sensor 10 (see FIG. 1). In this case, the output of the third AD converter 68 is a value that matches the sensor output of the oxygen sensor 10. Under such circumstances, the ECU 20 detects a digital signal generated by the third AD converter 68 every predetermined period (for example, every 4 msec), and acquires information on the oxygen concentration in the exhaust gas based on the detected value.

(Element impedance Rs calculation process)
FIG. 2 is a timing chart for explaining the operation of the ECU 20 realized in the mode for calculating the element impedance Rs of the oxygen sensor 10. More specifically, FIGS. 2A and 2B are waveforms showing the states of the first port 24 and the second port 44, respectively. 2C to 2E are waveforms representing changes in potential supplied to the input terminals of the first to third AD converters 32, 54, and 68, respectively.

  In principle, the ECU 20 turns off the second port 44 in the element impedance Rs calculation mode (see FIG. 2B). In this case, the second switch element 42 is turned off, and a state in which only the first capacitor 31 is connected in parallel to the series circuit of the first resistor 30 and the sensor element 10 is formed in the ECU 20. . Hereinafter, the parallel circuit formed by these elements is referred to as “R1 · Rs-C1 parallel circuit”. The ECU 20 includes an output detection resistor 52 connected in parallel with the oxygen sensor 10, but its resistance value (for example, 1.5 MΩ) is smaller than the element impedance Rs (several tens KΩ or less) of the oxygen sensor 10. Since it is large enough, it can be ignored here.

  When the calculation of the element impedance Rs is requested, the ECU 20 turns on the first port 24 at that time while keeping the second port 44 off (see FIG. 2A). When the first port 24 is turned on, the first switch element 22 is turned on, and the power supply voltage 5V starts to be applied to the second resistor 26. This voltage acts on the first sampling point 28 through the second resistor 26 and is applied to the R1 · Rs-C1 parallel circuit.

When the above voltage starts to be applied to the first sampling point 28, the potential VS1 at that point thereafter increases with the time constant τ, and finally the resistance value R2 of the second resistor 26, 1 converges to a value determined by the partial pressure of the resistance 30 and the combined resistance value R1 + Rs of the oxygen sensor 10. In this case, the convergence value VS1 and the time constant τ can be expressed by the following equation (1) or (2), respectively.
VS1 = 5 ・ (R1 + Rs) / (R2 + R1 + Rs) (1)
τ = C1 / {1 / (Rs + R1) + 1 / R2} (2)

  In the circuit shown in FIG. 1, the potential VS <b> 1 at the first sampling point 28 is supplied to the first AD converter 32. For this reason, the output of the first AD converter 32 shows the same change as VS1 expressed by the above equations (1) and (2). The waveform shown in FIG. 2C shows a state in which the output of the first AD converter 32 changes in such a manner after the first port 24 is turned on.

In the process of changing the potential VS1 of the first sampling point 28 as described above, a current I represented by the following formula flows through the oxygen sensor 10.
I = VS1 / (R1 + Rs) (3)

At this time, the potential VS2 of the second sampling point 50 can be expressed as follows using the current I and the element impedance Rs.
VS2 = Rs · I (4)

  Since the potential VS1 of the first sampling point 28 changes with the time constant τ, the current I satisfying the relationship of the above expression (3) is also the potential VS2 of the second sampling point 50 satisfying the relationship of the above expression (4). Also change with the time constant τ. In the circuit shown in FIG. 1, the potential VS2 of the second sampling point 50 is supplied to the second AD converter 54. Therefore, the output of the second AD converter 54 shows the same change as VS2 expressed by the above equations (4) and (2). The waveform shown in FIG. 2D shows a state in which the output of the second AD converter 54 has changed in such a manner after the first port 24 is turned on.

The current I flowing through the oxygen sensor 10 can be expressed as follows by using the potential VS1 of the first sampling point 28, the potential VS2 of the second sampling point 50, and the resistance value R1 of the first resistor 30. it can.
I = (VS1-VS2) / R1 (5)

From the above equations (4) and (5), the element impedance Rs can be expressed as the following equation.
Rs = VS2 / I
= VS2 / R1 / (VS1-VS2) (6)

  As described above, in the circuit of this embodiment, the element impedance Rs of the oxygen sensor 10 is based on the potentials VS1 and VS2 generated at the first sampling point 28 and the second sampling point 50 after the first port 24 is turned on. Can be calculated. By the way, the potential VS1 of the first sampling point 28 and the potential VS2 of the second sampling point 50 after the first port 24 is turned on are not limited to the leakage current generated before the first port 24 is turned on. The effect is superimposed. Therefore, in order to calculate the element impedance Rs with high accuracy, it is desirable to eliminate the influence of the leakage current and the like.

Therefore, the ECU 20 has a potential VS1 immediately before the first port 24 is turned ON (hereinafter referred to as “VS1OFF”) and a potential VS1 after the first port 24 is turned ON (hereinafter referred to as “VS1ON”). The difference ΔVS1 is obtained, and the potential VS2 immediately before the first port 24 is turned on (hereinafter referred to as “VS2OFF”) and the potential VS2 after the first port 24 is turned on (hereinafter referred to as “VS2ON”). The element impedance Rs is calculated according to the following equation by obtaining the difference ΔVS2 between the two and applying them to the above equation (6).
Rs = ΔVS2 ・ R1 / (ΔVS1−ΔVS2)
= (VS2ON-VS2OFF) · R1 / {(VS1OFF-VS1ON)-(VS2OFF-VS2ON)}
... (7)

  However, when the influence of the leakage current or the like is small and VS1OFF and VS2OFF are almost equal, it is not always necessary to use the relationship of the above equation (7). In that case, the element impedance Rs may be calculated according to the above equation (6) (assuming VS1 = VS1ON and VS2 = VS2ON).

  As described above, the ECU 20 can detect the potential of the first sampling point 28 by the first AD converter 32 and can detect the potential of the second sampling point 50 by the second AD converter 54. Therefore, when the calculation of the element impedance Rs is required, the ECU 20 specifically performs the calculation according to the following procedure.

(i) Immediately before the first port 24 is turned ON, the output of the first AD converter 32 is detected as VS1OFF, and the output of the second AD converter 54 is detected as VS2OFF.
(ii) After the above detection is completed, the first port 24 is turned on.
(iii) When a period (for example, 135 μsec) for VS1 to reach the convergence value after the first port is turned on, the output of the first AD converter 32 is detected as VS1ON, and the second AD The output of the converter 54 is detected as VS2ON.
(iv) After the above detection is completed, the first port 24 is returned to the OFF state.
(v) The element impedance Rs is calculated by substituting VS1OFF, VS1ON, VS2ON and VS2ON detected by the processes (i) to (iii) into the above equation (7).

[Explanation of problems associated with the calculation of element impedance Rs]
FIG. 3 shows an equivalent circuit diagram when the characteristics of the oxygen sensor 10 are faithfully represented. As shown in this figure, the oxygen sensor 10 has a capacitive component in addition to the electromotive force component and the impedance component. When a voltage is applied to a circuit composed of such components, charges are stored in the capacitive component. Until the stored charge is discharged, even after the voltage application to the oxygen sensor 10 is stopped, the voltage generated between the terminals of the oxygen sensor 10 is higher than the voltage generated by the electromotive force component. It becomes. That is, the sensor output (output voltage) of the oxygen sensor 10 becomes an excessive value with respect to the oxygen concentration in the exhaust gas until the electric charge stored in the capacitive component is discharged.

  FIG. 4 shows the waveform of the sensor output before and after the voltage is applied to the oxygen sensor 10 in order to calculate the element impedance Rs. A waveform indicated by a broken line in the figure is a sensor output waveform when the charge stored in the oxygen sensor 10 is naturally discharged after the first port 24 is turned off. Further, the waveform indicated by the solid line in the figure is a sensor output waveform when the charge stored in the oxygen sensor 10 is forcibly discharged immediately after the first port 24 is switched from ON to OFF. In the circuit configuration shown in FIG. 1, the charge stored in the oxygen sensor 10 can be forcibly discharged by turning on the second port 44, that is, by turning on the second switch element. More specifically, the waveform indicated by the solid line in FIG. 4 is a waveform obtained when the second port 44 is turned ON for a predetermined period immediately after the first port 24 is turned OFF from ON.

  As indicated by a broken line in FIG. 4, when the charge stored in the oxygen sensor 10 is spontaneously discharged, the voltage application to the oxygen sensor 10 is stopped for a while (here, for three sampling periods). The sensor output becomes an excessive value with respect to the output generated by the oxygen sensor 10 itself. Such an excessive sensor output (output indicated by x) does not correspond to the oxygen concentration in the exhaust gas, and therefore the output should not be used as a basis for obtaining information on the oxygen concentration.

  On the other hand, when the electric charge stored in the oxygen sensor 10 is forcibly discharged, that is, when the second port 44 is turned on for a predetermined period, as shown by the solid line in FIG. After the voltage application is stopped, the sensor output immediately passes through the ground potential and converges to the original output. In this case, immediately after the voltage application to the oxygen sensor 10 is stopped, the sensor output of the oxygen sensor 10 becomes a value that correctly corresponds to the oxygen concentration in the exhaust gas. Therefore, the ECU 20 turns on the first port 24 to calculate the element impedance Rs and then turns on the second port 44 for a predetermined period to forcibly discharge the charge stored in the oxygen sensor 10. did.

  2A and 2B show a state in which the second port 44 is turned on at the same time as the first port 24 is turned off, and the second port 44 is turned off after a predetermined period. In the present embodiment, the ECU 20 captures the output of the oxygen sensor 10 supplied to the third AD converter 68 at a sampling period of 4 msec. 2C to 2E show that the first to third AD converters 32 are turned on when the second port is turned on as described above after the voltage starts to be applied to the oxygen sensor 10. , 54 and 68, the input voltage to the oxygen sensor 10 is converged to the original output generated by itself without waiting for 4 msec. When the input voltage to the third AD converter 68 shows such a change, all sensor outputs sampled by the ECU 20 correctly correspond to the oxygen concentration in the exhaust gas. For this reason, according to the system of the present embodiment, the information regarding the oxygen concentration in the exhaust gas is always detected correctly when the calculation process of the element impedance Rs ends without being affected by the voltage application for calculating the element impedance Rs. can do.

  FIG. 5 shows a flowchart of a control routine executed by the ECU 20 in order to realize the above function. Note that the routine shown in FIG. 5 is an interrupt routine that is started at each time (for example, every 4 msec) at which the output of the oxygen sensor 10 should be sampled.

In the routine shown in FIG. 5, first, the counter TCOUNT is counted up (step 100).
The counter TCOUNT is cleared every time the element impedance Rs calculation process is executed, and is a counter for counting the elapsed time thereafter.

Next, it is determined whether or not the count value of the counter TCOUNT has reached the element impedance calculation interval T1 (step 101).
As a result, when it is determined that TCOUNT ≧ T1 is not established, the processing cycle of this time is ended after the output of the oxygen sensor 10 is taken in by the third AD converter 68 (after the AD is taken in) ( Step 102).
According to the above processing, after the calculation processing of the element impedance Rs is completed and until TCOUNT ≧ T1, the output of the oxygen sensor 10 represents information on the oxygen concentration in the exhaust gas at every sampling timing. Captured as a thing.

If it is determined in step 101 that TCOUNT ≧ T1 is established, element impedance Rs calculation processing is executed at that time, and the counter TCOUNT is cleared to zero (step 104).
In the process of calculating the element impedance Rs, specifically, the above-described processes (i) to (v), that is, the first port 24 is turned on and a voltage is applied to the oxygen sensor 10, and VS1 and VS2 generated at that time are generated. A process for calculating the element impedance Rs is executed based on the change in.

When the calculation process of the element impedance Rs is completed and the first port 24 is turned off, the ON time of the second port 44 is calculated (step 106).
As described above, after calculating the element impedance Rs, the ECU 20 turns on the second port 44 in order to forcibly discharge the electric charge stored in the oxygen sensor 10. At this time, it is desirable that the second port 44 is quickly turned off after the forced discharge of the charge is completed. Therefore, in this step 106, the ON time necessary for the forced discharge of charge is set.

  FIG. 6 is a diagram for explaining the procedure for setting the ON time of the second port 44 in step 106. The diagram shown on the left side in FIG. 6 is a map that defines the relationship between the element impedance Rs and the ON time of the second port 44. In addition, in FIG. 6, the diagram shown on the right side is a map that defines the relationship between the sensor output generated by the oxygen sensor 10 by its own electromotive force and the ON time of the second port 44. In step 106, a time obtained by multiplying the ON times determined by these two maps is set as the ON time of the second port 44.

  According to the map shown in FIG. 6, the ON time of the second port 44 is set to be longer as the element impedance Rs is larger. When the first port 24 is turned on and a voltage is applied to the oxygen sensor 10, the potential reached increases as the element impedance Rs increases. The charge stored in the oxygen sensor 10 becomes larger as the above-mentioned potential is higher. For this reason, in order to forcibly discharge the charge after the first port 24 is turned off, the longer the element impedance Rs, the longer the time required. According to the processing of step 106, the ON time of the second port can be set so that such a request is satisfied.

  Further, according to the map shown in FIG. 6, the ON time of the second port 44 is set to be shorter as the sensor output normally generated by the oxygen sensor 10 is higher. After the first port 24 is turned off and the voltage application to the oxygen sensor 10 is stopped, the sensor output of the oxygen sensor 10 becomes the normal output earlier as the difference between the output at the time of voltage application and the normal output is smaller. Easy to return. That is, in this embodiment, the higher the normal sensor output of the oxygen sensor 10 is, the more the sensor output returns to the normal value earlier after the first port 24 is turned off. Therefore, it is desirable to set the ON time of the second port 44 to a shorter time as the normal sensor output of the oxygen sensor 10 is higher. According to the processing in step 106, the ON time of the second port can be set so as to satisfy such a request.

In the routine shown in FIG. 5, next, the ON process of the second port 44 is executed (step 108).
Here, specifically, a process of turning on the second port 44 for the ON time set in step 106 is executed. By executing the processing of step 108, the sensor output of the oxygen sensor 10 is a normal output immediately after the first port 24 is turned off, that is, an output that correctly represents the state of the oxygen concentration in the exhaust gas. Return to.

  When the sampling timing comes again after the processing of step 108 is completed, it is determined that the condition of step 101 is not satisfied, and the processing of step 102 is executed again. The sensor output of the oxygen sensor 10 has returned to the normal output before that time. For this reason, the ECU 20 can correctly detect the sensor output corresponding to the oxygen concentration in the exhaust gas from the sampling timing immediately after calculating the element impedance Rs.

  As described above, according to the routine shown in FIG. 5, the charge stored in the oxygen sensor 10 in the process of calculating the element impedance Rs can be forcibly discharged by turning on the second port 44. . And according to this routine, the information regarding the oxygen concentration in exhaust gas can be correctly detected for every sampling timing, without being influenced by the voltage application accompanying calculation of element impedance Rs. For this reason, according to the apparatus of this embodiment, it is possible to realize both a function of correctly detecting the element impedance Rs of the oxygen sensor 10 and a function of accurately detecting information related to the oxygen concentration in the exhaust gas.

  By the way, in Embodiment 1 mentioned above, when calculating element impedance Rs, a positive voltage is applied to the positive terminal of the oxygen sensor 10, and then the potential of the positive terminal of the oxygen sensor 10 is lowered (grounded). However, the method for quickly returning the sensor output to the normal output is not limited to this. That is, when the element impedance Rs is calculated, a negative voltage may be applied to the negative terminal of the oxygen sensor 10 and then the potential of the negative terminal of the oxygen sensor may be raised to quickly return the sensor output. .

  In the first embodiment described above, the voltage applied to the oxygen sensor 10 is set to zero V in order to quickly return the sensor output after the voltage is applied to the oxygen sensor 10. The invention is not limited to this. That is, the voltage applied to the oxygen sensor 10 in order to quickly return the sensor output is the sensor output (output voltage) normally generated by the oxygen sensor 10 or the voltage applied to calculate the element impedance Rs as seen from the output voltage. Any reverse voltage may be used.

  In the first embodiment described above, the control target of the ECU 20 is limited to an oxygen sensor (a sensor that generates an output according to whether the exhaust air-fuel ratio is rich or lean). It is not limited to. That is, the present invention is not limited to the oxygen sensor, and may be applied to an air-fuel ratio sensor that generates an output representing the oxygen concentration (air-fuel ratio) in the gas to be detected.

In the first embodiment described above, the ON time of the second port 44 corresponds to the “predetermined time” in the first aspect of the invention, and the ECU 20 executes the processing of step 104 described above. The “impedance detecting means” in the first invention realizes the “reverse voltage applying means” in the first invention by executing the processing of step 108 described above.
In the first embodiment described above, the “reverse voltage application period setting means” according to the first or second aspect of the present invention is realized by the ECU 20 executing the processing of step 106.

Embodiment 2. FIG.
Next, a second embodiment of the present invention will be described with reference to FIGS.
The system of the present embodiment can be realized by causing the ECU 20 to execute a routine shown in FIG. 8 to be described later instead of the routine shown in FIG. 5 using the configuration shown in FIG.

  In the first embodiment described above, after applying a voltage to the oxygen sensor 10 to calculate the element impedance Rs, the electric charge stored in the oxygen sensor 10 is forcibly discharged, so that the oxygen concentration in the exhaust gas is correctly set. Incorporation of sensor output that is not supported is to be prevented. On the other hand, in the system of the present embodiment, after a voltage is applied to the oxygen sensor 10, the sensor output is not captured as a normal value during a period in which the influence of the voltage application remains on the sensor output. It is characterized in that it prevents the sensor output including errors from being taken in.

  FIG. 7 shows changes in the sensor output before and after the voltage for calculating the element impedance Rs is applied to the oxygen sensor 10. A waveform indicated by a broken line in FIG. 7 indicates a waveform in the case where the element impedance Rs is large and the sensor output greatly increases with voltage application. In addition, the waveform indicated by the solid line in FIG. 7 is a waveform in the case where the element impedance Rs is small and the increase in sensor output due to voltage application is small.

  As shown in FIG. 7, when the oxygen sensor 10 has a large element impedance Rs (in the case of a broken line), the sensor output increases with voltage application, and then the value is the original value, that is, in the exhaust gas. It takes a relatively long period to decrease to a value corresponding to the oxygen concentration. Further, when the element impedance Rs of the oxygen sensor 10 is small, the sensor output returns to the original value in a relatively short time after voltage application. For this reason, if the sensor output is sampled at a constant interval, the number of sensor outputs including errors, that is, the number of acquisitions of data to be discarded in the present embodiment is The number is larger than when the value Rs is small. Therefore, in the present embodiment, the ECU 20 applies a voltage to the oxygen sensor 10 to calculate the element impedance Rs, and then converts the sampled data (sensor output) to an error according to the calculated number of times according to the element impedance Rs. It is supposed to be discarded as containing.

  FIG. 8 shows a flowchart of a control routine executed by the ECU 20 in the present embodiment in order to realize the above function. In FIG. 8, steps that are the same as the steps shown in FIG. 5 are given the same reference numerals, and descriptions thereof are omitted or simplified.

In the routine shown in FIG. 8, when it is determined in step 101 that the element impedance Rs calculation interval T1 has elapsed (TCOUNT ≧ T1 is established), the processing in step 104 (element impedance Rs calculation, and After the completion of the counter TCOUNT), the data discard count AD1 is calculated (step 110).
FIG. 9 shows an example of a map that defines the relationship between the number of data discards AD1 and the element impedance Rs. The ECU 20 stores a map as shown in FIG. 9, and in this step 110, by referring to this map, the number of data discards corresponding to the element impedance Rs calculated in the above step 104 is calculated. According to the map shown in FIG. 9, the data discard count AD1 can be set to a larger value as the element impedance Rs is larger and the influence of voltage application is more likely to remain in the sensor output.

In the routine shown in FIG. 8, next, the counter ADCOUNT is cleared (step 112).
ADCOUNT is a counter for counting the number of times the sensor output is executed after the element impedance Rs calculation process. When the processing of this step 112 is completed, the ECU 20 ends the current processing cycle.

In the routine shown in FIG. 8, if it is determined in step 101 that TCOUNT ≧ T1 is not established, the sensor output is sampled in step 102, and then the counter ADCOUNT is incremented (step 114).
According to the above processing, until the element impedance calculation interval T1 elapses, the sensor output is sampled at every sampling interval (every time the routine is started), and the count value of the counter ADCOUNT is incremented. it can.

In the routine shown in FIG. 8, it is next determined whether or not the count value of the counter ADCOUNT is equal to or less than the data discard count AD1 (step 116).
As a result, while it is determined that ADCOUNT ≦ AD1, the sensor output (data) sampled in step 102 is discarded (step 118).
If it is determined that ADCOUNT ≦ AD1 does not hold, the processing of step 118 is jumped, and the current processing cycle is terminated without discarding the fetched data.

  As described above, according to the routine shown in FIG. 8, after a voltage is applied to the oxygen sensor 10 to calculate the element impedance Rs, the sampled sensor output is output for a predetermined data discard count AD1. Can be discarded. The data discard count AD1 can be set to correspond to a period in which an error is expected to be superimposed on the sensor output based on the element impedance Rs. For this reason, according to the system of the present embodiment, it is possible to realize both the function of calculating the element impedance Rs of the oxygen sensor 10 and the function of always detecting information on the oxygen concentration in the exhaust gas with high accuracy.

  In the second embodiment described above, the data discard count AD1 is set based on the element impedance Rs of the oxygen sensor 10. However, the setting method is not limited to this, and AD1 is set as follows. When setting, the normal sensor output value of the oxygen sensor 10 may be considered as in the case of the first embodiment. More specifically, the number of data discards is such that the difference between the normal sensor output value of the oxygen sensor 10 and the reached value of the sensor output at the time of voltage application is so small that the time required for data convergence is short. Alternatively, a small value may be set.

  In the second embodiment described above, the control target of the ECU 20 is limited to an oxygen sensor (a sensor that generates an output according to whether the exhaust air-fuel ratio is rich or lean). It is not limited to. That is, the present invention is not limited to the oxygen sensor, and may be applied to an air-fuel ratio sensor that generates an output representing the oxygen concentration (air-fuel ratio) in the gas to be detected.

In the second embodiment described above, the period corresponding to the data discard count AD1 corresponds to the “predetermined period” in the third aspect of the invention, and the ECU 20 executes the process of step 104 above. "impedance detection means" according to the third invention, the "data discarding means" according to the third embodiment is realized by executing the process of step 118 is implemented, respectively.
In the second embodiment described above, the “data discard period setting means” according to the third aspect of the present invention is implemented when the ECU 20 executes the processing of step 110 described above.

Embodiment 3 FIG.
Next, Embodiment 3 of the present invention will be described with reference to FIG. 10 and FIG.
The system of the present embodiment can be realized by causing the ECU 20 to execute a routine shown in FIG. 11 described later instead of the routine shown in FIG. 5 using the configuration shown in FIG.

  In the present embodiment, the ECU 20 executes a process for calculating the element impedance Rs every time the element impedance calculation interval T1 elapses, as in the case of the first embodiment described above. When the element impedance Rs is calculated, a voltage is applied to the oxygen sensor 10 as described above. The output of the oxygen sensor 10 has a value that does not accurately correspond to the oxygen concentration in the exhaust gas until the influence of the voltage application disappears. For this reason, information on the oxygen concentration in the exhaust gas can be accurately detected based on the sensor output until the element impedance calculation interval T1 elapses after the influence of voltage application disappears from the sensor output. Limited in time.

  The time required for the influence of voltage application to disappear from the sensor output of the oxygen sensor 10 increases as the element impedance Rs increases. For this reason, if the element impedance calculation interval T1 is constant, if the element impedance Rs is small, the element impedance Rs can be sufficiently ensured while the information on the oxygen concentration in the exhaust gas can be properly detected. Under large circumstances, such a period cannot be secured.

  FIG. 10 is a timing chart for explaining operations realized in the present embodiment in order to cope with the above situation. Specifically, FIG. 10A shows a sensor output waveform of the oxygen sensor 10 realized when the element impedance Rs is large. FIG. 10B shows a waveform of the sensor output of the oxygen sensor 10 realized when the element impedance Rs is small. 10A and 10B, the period indicated as T1 is the above-described element impedance calculation period. A period indicated as T2 is a period during which sensor output sampling is prohibited.

  As shown in FIGS. 10A and 10B, in the system of this embodiment, when the element impedance Rs is large, the element impedance calculation interval T1 is set long, and the sampling inhibition period T2 is lengthened. Set. When the element impedance Rs is small, the element impedance calculation interval T1 is set short, and the sampling prohibition period T2 is set short. When T1 and T2 are set in this way, a sufficient period for obtaining normal sensor output is ensured regardless of the length of time during which the influence of voltage application for calculating element impedance Rs disappears from the sensor output. be able to. For this reason, according to the system of the present embodiment, information regarding the oxygen concentration in the exhaust gas can always be detected appropriately regardless of the element impedance Rs of the oxygen sensor 10.

  FIG. 11 shows a flowchart of a control routine executed by the ECU 20 for realizing the above function. In FIG. 11, the same steps as those shown in FIG. 5 or FIG. 8 are denoted by the same reference numerals, and the description thereof is omitted or simplified.

In the routine shown in FIG. 11, the element impedance calculation interval T1 and the sampling prohibition period T2 are set together with the counting up of the counter TCOUNT (step 120).
In the present embodiment, the ECU 20 stores a map that defines T1 and a map that defines T2 in relation to the element impedance Rs. In step 120, T1 and T2 are set by referring to these maps.

  When the process of step 120 is completed, the process of step 100, that is, the process of determining whether TCOUNT ≧ T1 is satisfied is executed. If it is determined that this condition is satisfied, the element impedance Rs is calculated and the counter TCOUNT is cleared in step 104, and then the current processing cycle is terminated. On the other hand, if it is determined that the above condition is not satisfied, it is determined whether or not TCOUNT ≧ T2 is satisfied (step 122).

  If it is determined that TCOUNT ≧ T2 does not hold, it can be determined that the sampling prohibition period T2 has not yet elapsed after the element impedance Rs is calculated. In the routine shown in FIG. 11, in this case, the current processing cycle is terminated without sampling the sensor output. On the other hand, if it is determined that TCOUNT ≧ T2 is established, it can be determined that the sampling prohibition period T2 has already elapsed. In this case, after that, after the sensor output is sampled in step 102, the current processing cycle is terminated. According to these processes, the sensor output can be taken in every sampling interval only after the sampling inhibition period T2 elapses and until the element impedance calculation interval T1 elapses.

  Both the map relating to T1 and the map relating to T2 used in step 120 are set so that the larger the element impedance Rs, the larger the value of T1 or T2. More specifically, the map relating to the element impedance calculation interval T1 is a relationship between Rs and T1 so that the period during which the oxygen sensor 10 generates a normal sensor output is always sufficiently secured regardless of the value of the element impedance Rs. Is stipulated. In addition, the map related to the sampling prohibition period T2 is determined in relation to the element impedance Rs so that the period in which the influence of voltage application remains on the sensor output of the oxygen sensor 10 becomes the sampling prohibition period T2. . Therefore, according to the routine shown in FIG. 11, it is possible to always ensure a sufficient period for the oxygen sensor 10 to emit a normal output regardless of the value of the element impedance Rs, and to sample only the correct sensor output. Can do. Therefore, according to the system of the present embodiment, it is possible to realize both the function of accurately detecting the element impedance Rs and the function of accurately detecting information related to the oxygen concentration in the exhaust gas.

  In the second embodiment described above, the element impedance calculation interval T1 and the sampling prohibition period T2 are set based on the element impedance Rs. However, the setting method is not limited to this, When setting them, the normal sensor output value of the oxygen sensor 10 may be considered as in the case of the first embodiment. More specifically, each of T1 and T2 is expected to have a small difference between the normal sensor output value of the oxygen sensor 10 and the reached value of the sensor output when a voltage is applied, and the time required for data convergence is short. The smaller the value, the better.

  Further, in the above-described third embodiment, the ECU 20 is limited to the oxygen sensor (sensor that generates an output depending on whether the exhaust air-fuel ratio is rich or lean). It is not limited to. That is, the present invention is not limited to the oxygen sensor, and may be applied to an air-fuel ratio sensor that generates an output representing the oxygen concentration (air-fuel ratio) in the gas to be detected.

In the third embodiment described above, the element impedance calculation interval T1 corresponds to the “predetermined interval” in the fourth aspect of the invention, and the ECU 20 executes the processing of step 104 above to execute the fourth step. The “impedance detection means” in the present invention realizes the “impedance detection interval setting means” in the fourth invention by executing the processing of step 120 described above.
In the above-described third embodiment, the sampling prohibition period T2 corresponds to the “predetermined period” in the fifth aspect of the invention, and the ECU 20 executes the processing of steps 100 and 122 described above. It is "output acquisition period setting means" 5 in the invention of "egress-acquisition period setting means" in the fifth aspect of the present invention by executing the process of step 120 is implemented, respectively.

Embodiment 4 FIG.
Next, a fourth embodiment of the present invention will be described with reference to FIGS.
The system of the present embodiment can be realized by causing the ECU 20 to execute a routine shown in FIG. 14 described later in place of the routine shown in FIG. 11 in the apparatus of the third embodiment.

  As described above, the device according to the third embodiment increases the element impedance calculation interval T1 as the element impedance Rs increases. FIG. 12 is an example of a map of the element impedance calculation interval T1 that can be used in the apparatus of the third embodiment as satisfying such setting (see step 120 in FIG. 11). According to this map, in the region where the element impedance Rs is sandwiched between the upper convergence value RsH and the lower convergence value RsL, the element impedance calculation interval T1 is determined so as to show a linear relationship with the element impedance Rs, and the element impedance Rs In the region where the value exceeds the upper convergence RsH and the region below the lower convergence value RsL, the element impedance calculation interval T1 is determined to be a predetermined upper limit value T1max or a lower limit value T1min, respectively. In this case, the interval at which the voltage for detecting the element impedance Rs is applied to the oxygen sensor 10 becomes longer as the element impedance Rs is larger, and becomes shorter as the element impedance Rs is smaller.

  FIG. 13 is a diagram showing the relationship between the element temperature of the oxygen sensor 10 and the element impedance Rs. As shown in this figure, the element impedance Rs becomes a small value as the element temperature of the oxygen sensor increases. When a voltage for detecting element impedance is applied to the oxygen sensor 10, the current I flowing through the oxygen sensor 10 increases as the element impedance Rs decreases. For this reason, the current I increases as the element temperature of the oxygen sensor 10 increases.

  According to the map shown in FIG. 12, when the element impedance Rs falls below the downward convergence value RsL, that is, when a large current I flows during voltage application, the element impedance calculation interval T1 is the lower limit value. Is done. In this case, the element impedance Rs is frequently detected, and as a result, a large amount of current I is frequently circulated through the oxygen sensor 10. The oxygen sensor 10 is greatly damaged as the current I flowing therethrough is increased and the circulation time of the current I is increased. For this reason, if the element impedance calculation interval T1 is determined according to a map as shown in FIG. 12, the oxygen sensor 10 is likely to be greatly damaged after the element temperature has sufficiently increased. Therefore, in the present embodiment, in a region where the element impedance Rs is sufficiently low, the element impedance calculation interval T1 is set to a large value in order to reduce the frequency of voltage application to the oxygen sensor 10.

  FIG. 14 shows a flowchart of a control routine executed by the ECU 20 in the present embodiment in order to realize the above function. The routine shown in FIG. 14 is the same as the routine shown in FIG. 11 except that step 120 is replaced with step 130. In FIG. 14, the same steps as those shown in FIG. 11 are denoted by the same reference numerals, and the description thereof is omitted or simplified.

  In the routine shown in FIG. 14, in step 130, a) the counter TCOUNT is counted up, b) the element impedance calculation interval T1 is set, and c) the sampling inhibition period T2 is set. Among these processes, the processes a) and c) are performed in the same manner as in the third embodiment (see FIG. 11; step 120). Then, b) the element impedance calculation interval T1 is set with reference to the map shown in FIG.

  FIG. 15 shows an example of a map that the ECU 20 stores in order to set the element impedance calculation interval T1 in the present embodiment. A predetermined threshold RsTH smaller than the downward convergence value RsL is set on the horizontal axis of the map shown in FIG. This map is set similarly to the map shown in FIG. 12 in the region where the element impedance Rs exceeds the threshold value RsTH. The map shown in FIG. 15 is set so that the element impedance calculation interval T1 rapidly becomes the upper limit value T1max as the sensor impedance Rs decreases in the region where the element impedance Rs falls below the threshold value RsTH. .

  The threshold value RsTH shown in FIG. 15 is a value set as the minimum element impedance Rs that does not unreasonably damage the oxygen sensor 10 when the element impedance calculation interval T1 is the lower limit value T1min. That is, according to the map shown in FIG. 15, when the element impedance Rs of the oxygen sensor 10 becomes RsTH, the element impedance calculation interval T1 is determined to be the lower limit value T1min. In this case, a voltage for detecting element impedance is repeatedly applied to the oxygen sensor 10 at intervals of the lower limit value T1min. With each voltage application, a current I = V / RsTH corresponding to a value obtained by dividing the applied voltage V by RsTH flows through the oxygen sensor 10. The threshold value RsTH is an element impedance Rs that generates the maximum current I that can be repeatedly circulated at intervals of T1 min without undue damage to the oxygen sensor 10.

  According to the routine shown in FIG. 14, the element impedance Rs detection process is repeated at the element impedance calculation interval T1 set according to the map shown in FIG. In this case, the damage to the oxygen sensor 10 due to voltage application is when the element impedance Rs matches the threshold value RsTH due to the relationship between the voltage application interval (T1) and the current I generated by voltage application. It will be the biggest one. The threshold value RsTH is set so that the damage received by the oxygen sensor 10 in such a case does not become unreasonably large as described above. For this reason, in this embodiment, no matter what value the element impedance Rs has, the oxygen sensor 10 will not be unduly damaged by repeating the detection process of the element impedance Rs.

  As described above, the apparatus of the present embodiment prevents the oxygen sensor 10 from being inappropriately damaged by reducing the frequency of detection of the element impedance Rs in a region where the element impedance Rs of the oxygen sensor 10 is sufficiently small. Can do. For this reason, according to the apparatus of this embodiment, while achieving the effect similar to the apparatus of Embodiment 3, the effect that deterioration of the oxygen sensor 10 can fully be suppressed can also be achieved.

In the fourth embodiment described above, ECU 20 is, in step 130, by determining the element impedance calculation interval T1 by referring to a map shown in FIG. 15, set "impedance detection interval in the invention of the sixth Means "and" Low impedance detection interval setting means " are realized.

It is a figure for demonstrating the structure of Embodiment 1 of this invention. 2A to 2E are timing charts for explaining operations realized in the first embodiment of the present invention. It is an equivalent circuit schematic of the oxygen sensor shown in FIG. It is a figure which shows the waveform of the sensor output before and behind the voltage being applied with respect to the oxygen sensor shown in FIG. It is a flowchart of the control routine performed in Embodiment 1 of the present invention. It is a figure for demonstrating the method used when calculating the ON time of a 2nd port in the routine shown in FIG. It is the figure which represented the waveform of the sensor output before and after the voltage was applied with respect to the oxygen sensor shown in FIG. 1 by the relationship with element impedance Rs. It is a flowchart of the control routine performed in Embodiment 2 of the present invention. It is a figure which shows an example of the map referred when calculating the data discard frequency AD1 in the routine shown in FIG. FIGS. 10A and 10B are timing charts for explaining the outline of the operation realized in the third embodiment of the present invention. It is a flowchart of the control routine performed in Embodiment 3 of the present invention. It is an example of the map of the element impedance calculation space | interval T1 which can be used in Embodiment 3 of this invention. It is a figure which shows the relationship between the element temperature of the oxygen sensor shown in FIG. 1, and element impedance Rs. It is a flowchart of the control routine performed in Embodiment 4 of the present invention. 15 is an example of a map of element impedance calculation intervals T1 referred to in the control routine shown in FIG.

Explanation of symbols

10 Oxygen sensor 20 ECU (Electronic Control Unit)
22 1st switch element 24 1st port 26 2nd resistance 28 1st sampling point 30 1st resistance 42 2nd switch element 44 2nd port 50 2nd sampling point
Rs Element impedance
RsTH threshold

Claims (6)

A control device for a gas concentration sensor that emits an output having a correlation with an oxygen concentration in a gas to be detected,
Impedance detection means for applying an impedance detection voltage to the gas concentration sensor to detect an element impedance of the gas concentration sensor;
After the impedance detection voltage is applied to the gas concentration sensor, the same voltage as that generated by the gas concentration sensor, or a voltage opposite to the impedance detection voltage as viewed from the voltage, is applied for a predetermined period. Reverse voltage applying means for applying to the gas concentration sensor;
Reverse voltage application period setting means for setting the predetermined period longer as the element impedance is larger;
A control device for a gas concentration sensor, comprising:   2. The gas concentration sensor according to claim 1, wherein the reverse voltage application period setting means sets the predetermined period to be shorter as a difference between the voltage generated by the gas concentration sensor and the impedance detection voltage is smaller. Control device. A control device for a gas concentration sensor that emits an output having a correlation with an oxygen concentration in a gas to be detected,
Impedance detection means for applying an impedance detection voltage to the gas concentration sensor to detect an element impedance of the gas concentration sensor;
Data discarding means for discarding the output of the gas concentration sensor for a predetermined period after the impedance detection voltage is applied to the gas concentration sensor;
Data discard period setting means for setting the predetermined period longer as the element impedance is larger;
A control device for a gas concentration sensor, comprising: A control device for a gas concentration sensor that emits an output having a correlation with an oxygen concentration in a gas to be detected,
Impedance detection means for detecting an element impedance of the gas concentration sensor by applying an impedance detection voltage to the gas concentration sensor at predetermined intervals;
Impedance detection interval setting means for setting the predetermined interval longer as the element impedance is larger;
A control device for a gas concentration sensor, comprising: Output acquisition period setting means for setting a period from when a predetermined period has elapsed after detection of the element impedance to when the impedance detection voltage is applied again to the gas concentration sensor as an output acquisition period of the gas concentration sensor When,
An output non-acquisition period setting means for setting the predetermined period to be longer as the element impedance is larger;
The gas concentration sensor control device according to claim 4, further comprising: The impedance detection interval setting means, the area wherein the element impedance is equal to or greater than a predetermined threshold value, which is set longer the predetermined distance as the element impedance is large,
Low-impedance detection interval setting means for setting the predetermined interval longer than a predetermined interval set when the element impedance matches the predetermined threshold in a region where the element impedance is lower than the predetermined threshold. control apparatus for a gas concentration sensor according to claim 4 or 5, wherein further comprising.

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